Hoping to put as many succulent plants as possible in GH because they are the ones that have the most difficulty getting enough sun inside during winter. A GH will keep them protected from rain and prolific dew, but won't be heated unless it's supposed to go below low 20's, temps that only last for a few hours during the coldest nights here.

Hoping those from more dry Z8 (or lower) climates would tell us what succulents they are able to have in outdoor gardens or left in pots outside all year.

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I kept an Agave Parryi Truncata very happy over last winter in a double-walled, plastic coldframe. I'm sure my other Agave Parryi JC Raulston would have been fine, or my Agave Ovatifolia, or my Agave Montana. There are plenty of cold hardy Agaves and since you'll have them in a greenhouse you can control the moisture which is more concerning to me as all of these Agaves are now in the garden soil. As you might guess, cold + wet can be a death sentence.
You might find this site informative:http://www.coldhardycactus.com/

I am in zone 8b/9a, southern California high desert. Our winters are pretty frigid, temps drop into the teens quite often and we get snow a few times a year usually (sometimes heavy). Lots of frost here. Besides lots of sempervivum, jovibarba, and opuntia, I have some lithops that manage quite well so long as they are bone dry and I bring them in on the coldest nights just to be safe. They just get plunked in my cold garage overnight and do fine. My aloe veras and 10 year old aloe ferox live outside all year in their pots, but come up onto my covered patio in winter and get covered with old blankets at night. One of my aloe veras was once forgotten outside on a frosty night unprotected and got a pretty good frost burn on a few leaves but survived. My adenium obesum spend the winter in my unheated garage. My echeverias and graptoverias overwinter in there as well even though it sometimes feels like an ice box. Surprising how many heat loving plants (my lemongrasses and lemon verbenas overwinter in my garage as well) can take low temps but I suspect that if I had them unprotected and in-ground, they would be toast after one hard frost.

Thanks for your input, much appreciated! Those sound like some very similar situations.

That's been my method too, no watering before/during a cold spell. Winter low temps here just depend on which way the wind is blowing. Some nights are in the high 40's, or there could be an ice storm, and quite a bit of rain is normal. Last winter was so mild that many plants that got frost-bitten foliage survived at the roots and have grown back so that they look fine, but would just never have a hope of getting to a mature size that way, and an unusually mild winter is not something to "bank on."

In a garage, shed, unheated GH, the temp might get as cold as outside the structure, but dew doesn't get on plants, therefore there's no actual frost on them. That seems to make a difference, from my casual observation.

Since I have at least 2 of about everything, I'm planning to have at least 1 of everything "important" in the house.

I've realized I'm only considering plants with origins in dry climates as candidates to use the GH space, vs. jungle epiphytes. Is that a consideration others use if faced with similar options?

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